The invention relates to a method of keeping track of the operating position of an actuator in an automated gear-shift transmission. Directed by a transmission control unit and working through a transfer mechanism connecting to internal shifter elements of the transmission, the actuator serves to select a gear stage that is to be engaged and/or to perform the engagement of the gear stage.
The invention also relates to a transmission control unit that is equipped with appropriate devices to perform the aforementioned inventive method.
Gear-shift transmissions for motor vehicles are known in many ways. In the past, the term xe2x80x9cgear-shift transmissionxe2x80x9d was primarily understood to mean a manually shiftable transmission which the driver of the vehicle would shift by hand through a shift lever. The shift movement in this kind of transmission is performed in a shift patternxe2x80x94a so-called shift gatexe2x80x94where the shift lever is first moved in a selector track to an intersection with an engagement track, whereupon the transmission is shifted into the new gear by pushing the shift lever into the selected engagement track.
In addition to manual transmissions of the kind that has just been described, the known state of the art also includes automated gear-shift transmissions in which actuators are coupled to the transmission to perform the movement along a selector track and then shift the transmission into gear by moving to the end of an engagement track. In an automated gear-shift transmission, the phases of selecting and engaging a gear are performed, e.g., through actuators under the control of a program. The actuators are connected through a transfer mechanism to internal shifter elements of the transmission such as for example a central shifter shaft and shifting rods.
In an automated gear-shift transmission, the process of selecting, engaging and disengaging the individual gear stages runs under the control of a program, which requires the actual operating position of the individual actuators, such as electric motors or hydraulic cylinders, to be known, because the positions of the shifter elements inside the transmission are tied directly to the operating positions of the actuators. It can therefore not be allowed to happen that the operating position of individual actuators becomes unavailable, e.g., because of a temporary failure in the electrical system of the vehicle.
The present invention therefore has the object of proposing a method of keeping the actual operating positions of the actuators continuously available for use by the program that controls the movements of the actuators.
The method according to the invention is designed to keep track of the operating position of an actuator in an automated gear-shift transmission. Directed by a transmission control unit and working through a transfer mechanism connecting to internal shifter elements of the transmission, the actuator serves to select a gear stage that is to be engaged and/or to move the selected gear stage into engagement. Under the inventive method, the energy source that powers the actuator is monitored, and if the energy level is found to be inadequate, the actuator position is stored so that it can be retrieved on demand.
In addition, the invention also proposes a transmission control unit that is appropriately equipped to perform the aforementioned inventive method.
According to the inventive method, a decrease in the energy level is detected at an early stage by monitoring the energy source of the actuator such as for example the system voltage of the vehicle, and by determining and storing the actual positions of the actuators, so that they can be retrieved at a later time when the energy level has come back to an adequate level. Thus, a time-consuming set-up process to establish a reference position of the actuator is made unnecessary.
According to an advantageous embodiment of the inventive method, the actuator position is stored by the transmission control unit. As a storage medium, one could use for an example an EEPROM (Electronically Erasable Programmable Read-Only Memory) in the transmission control unit, so that the actual positions of an actuator for the selecting movement and an actuator for the gear-engaging movement remain available after a complete breakdown of the system voltage of the vehicle. The method can be executed by the transmission control unit through a step of monitoring the system voltage of the vehicle and a step of determining and storing the actual actuator positions if the system voltage is found to have fallen to a predetermined threshold level.
The foregoing concept is advantageous for example, if the actuator is an electric motor using an incremental principle for measuring actuator displacement. The operating voltage of the motor is monitored and, if it falls below a predetermined threshold value, stored in the transmission control device.
The actual position that was registered and stored cannot be allowed to change after it has been saved in memory. A further developed version of the invention therefore includes the concept that the energy supply to the actuator is interrupted after detecting an energy level that is inadequate for powering the actuator. This feature of the inventive method is used advantageously, if the energy level is found to be declining gradually, indicating that within a short time the energy level will be insufficient to drive the actuators.
In a further embodiment of the method for keeping track of an actuator position in an automated gear-shift transmission, the actuator is likewise directed by a transmission control unit and works through a transfer mechanism connected to internal shifter elements of the transmission to select a gear stage that is to be engaged and/or to perform the engagement of the gear stage. The transmission control unit monitors the actual position of the actuator and can under certain conditions store the actual actuator position in memory. In the latter case, the transmission control unit will interrupt the energy supply to the actuator after the actuator position has been saved in memory.
The preceding embodiment of the method is used advantageously if the decline in the energy level occurs intentionally, for example when the electric system is deactivated for servicing the vehicle, e.g., by disconnecting the battery.
In the latter case, where the decline of the energy level is not gradual but occurs abruptly, it is advantageous to connect the transmission control unit to a diagnostic device that instructs the transmission control unit to store the actual operating position and to interrupt the energy supply.
After the actual positions of the actuators have been stored in memory, the supply voltage for the actuators and the transmission control unit can be interrupted. After the electric system of the vehicle has been reactivated, the transmission control unit can, for example, after detecting that the supply voltage has returned to an adequate level, automatically retrieve the actual positions that existed before the interruption of the electric supply and were saved, e.g., in an EEPROM. Alternatively, the retrieval of the saved actual position values could also be performed in response to an appropriate instruction from the diagnostic device to the transmission control unit.
The invention also provides a transmission control unit equipped with one or more devices for keeping track of the operating position of an actuator in an automated gear-shift transmission. The actuator is connected to the transmission control unit and works through a transfer mechanism acting on internal shifter elements of the transmission to select a gear stage that is to be engaged and/or to perform the engagement of the gear stage. The inventive transmission control unit monitors the energy source that powers the actuator and, if the energy level is found to be inadequate, the actuator position is stored so that it can be retrieved on demand.
For example, the transmission control unit can be equipped with a voltage sensor to monitor the voltage of the onboard electrical system of the vehicle, one or more incremental position-measuring devices to detect the actual positions of the actuators, and a memory device for saving the actuator positions, if the system voltage is found to be insufficient to power the actuators.
Monitoring of the onboard system voltage allows the detection of an imminent loss of electrical power before the voltage has become too low for a continued operation of the transmission control unit. The actual positions of the actuators are saved in memory in the transmission control unit before the onboard system voltage has become too low for the transmission control unit to continue working. To store the position data, the transmission control unit can be equipped with a non-volatile data-storage device, for example in the form of an EEPROM.
When the vehicle is serviced at a repair shop and the onboard electric power supply is interrupted, the actual position data of actuators using an incremental principle of position measurement can be safeguarded by issuing an instruction from a diagnostic instrument to the transmission control unit to save the actual position data in memory and to subsequently interrupt the supply or stop the supply of energy to the actuators, so that the actuators are immobilized in the positions that were saved in memory. After the onboard supply voltage has been restored, the saved position data are retrieved from memory, and the operation of the actuators can be resumed.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. However, the inventive method and transmission control unit themselves will be best understood from the following detailed description of a presently preferred specific embodiment with reference to the accompanying drawing.